During a medical intervention, realtime images that serve to navigate the instruments being used and on which the inserted medical instrument is discernible are obtained and presented with the aid of fluoroscopy. Although not showing any spatial three-dimensional details, said 2D fluoroscopic images are nonetheless quickly available and will minimize the patient's and physician's exposure to radiation. For improving navigation it is known to register preoperatively recorded 3D images with the 2D fluoroscopic images and underlay these in a suitable representation. The spatial information missing from the 2D fluoroscopic images is conveyed in this way. Combining registered 2D and 3D images will then improve the physician's orientation within the targeted volume.
The 3D image can be registered with the 2D fluoroscopic images employing different techniques that utilize natural landmarks or artificial landmarks applied to the body, or correlations specific to the equipment used. During said 2D/3D image registration it is determined from which direction the 3D volume encompassed by the 3D image has to be projected so it can be made to coincide with the 2D image. A problem with 2D/3D registration, particularly in the case of abdominal applications such as, for instance, liver biopsies, is that the preoperatively recorded 3D image is static, whereas respiratory movements are clearly discernible in the 2D fluoroscopic images. That leads to errors in the overlaid representation with the projected 3D image.